1. Field of the Invention
The present invention relates to a separator for a fuel cell in which an electrically conductive portion which includes an electrode surface portion is arranged to be surrounded by an insulating portion, to a fuel cell which sandwiches a membrane electrode assembly with said separator, and to a connection construction between a terminal on a cell voltage measurement device side and a terminal on a fuel cell side.
The present application claims the priority rights of Japanese Patent Application 2003-328917 filed upon 19 Sep. 2003 and Japanese Patent Application 2003-328919 filed upon 19 Sep. 2003, and incorporates the contents thereof herein by reference.
2. Background Art
There is a type of fuel cell which is made as a unit fuel cell (hereinafter termed a “unit cell”) in which, for example, a solid polymerelectrolyte layer is sandwiched between an anode side electrode and a cathode side electrode, and furthermore a separator is provided on the outside thereof.
In order to ensure that an appropriate voltage should be generated, during actual use, this type of fuel cell is often utilized in a fuel cell stack (hereinafter termed a “stack”) in which a plurality of said unit cells are stacked together; and, in such a case, it is necessary to measure the cell voltages in order to monitor the electrical generating state of each of the unit cells.
Since an electrically conductive material such as, for example carbon or a metal or the like is used for a prior art separator (hereinafter this will be termed an “electrically conductive separator”), it has been possible to measure the cell voltage from the outside easily, by forming a portion of the separator in the form of a cell voltage measurement terminal, or by opening a round hole in the outer peripheral surface of the separator, and by connecting one end of an output terminal to this round hole by a banana clip (Patent Document 1: Japanese Unexamined Patent Application, First Publication No. H9-283166).
However, in the case of utilizing a stack which employs this electrically conductive separator, due to the potential difference between the unit cells, since there is the possibility that leakage current (seepage) or an electrical short circuit may occur along a flow conduit for the cooling water (the cooling medium), accordingly the cooling water is required to be endowed with a high level of insulating characteristic, so that a necessity arises to provide an ion exchanger in order to eliminate electrically conductive ions.
As a countermeasure to this, in recent years, the plan has been put forward to utilize an electrically conductive material such as a metal or the like in the contacting portions in the electrodes (the electrode surface portions), and to utilize an insulating material in the portions which form the communication holes for the reaction gas and the cooling water at portions surrounding the electrode surface portions; in other words, a compound type separator has been proposed.
If the stack is made by using these compound type separators, since the cooling water edge surface distance (the insulating distance) between the unit cells becomes long, apart from a high degree of insulating characteristic no longer being required from the cooling water, it is also possible to suppress the generation of rust upon the metallic separators. Furthermore, it is possible effectively to prevent the occurrence of short circuiting with the outside, since the outer edge portions of the separators are made from an insulating material.
Since, in this manner, with said compound type separators, the outer sides in the surface direction of the electrode surface portions (the outer peripheral sides of the separators) are made with an insulating construction, accordingly there is the strong point that it is possible effectively to prevent the occurrence of electrical seepage due to the cooling water or shorting to the exterior; but, on the other hand, the accompanying shortcoming is also entailed that the measurement of the cell voltage becomes extremely difficult.
Due to this situation, there is a requirement for development of a technique in order to make it possible to observe the state of electrical generation by each unit cell, while preventing electrical seepage and short circuiting.